On the role of number of fixtures, surgical technique and timing of loading

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On the role of number of fixture, surgical technique and timing of

loading

Alf Eliasson

Department of Prosthetic Dentistry/Dental Materials Science Institute of Odontology

Folktandvården

P o stgraduate Dental Education Center

ÖREBROCOUNTY COUNCIL

Gothenburg 2008

On the role of number of fixture, surgical technique and timing of

loading

Alf Eliasson

Department of Prosthetic Dentistry/Dental Materials Science Institute of Odontology

Folktandvården

P o stgraduate Dental Education Center

ÖREBROCOUNTY COUNCIL

Gothenburg 2008

On the role of number of fixtures, surgical technique and timing of

loading

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Abstract

Aims: The aims of this thesis were to analyze reduced number of implants supporting full arch fixed mandibular prostheses and fixed partial dentures (FPDs), non-submerged healing and early loading in the edentulous mandible. A further aim was to evaluate fit of Computer Numerical Controlled (CNC) milled I-Bridge^® frameworks.

Material & Methods: Paper I. One hundred and nineteen patients rehabilitated with full arch mandibular prostheses supported by four implants were evaluated after a mean follow-up of 4.4 years. Paper II. A total of 178 patients provided with FPDs supported by two (n=92) or three implants (n=122) of whom 123 were evaluated after a mean follow-up of 9.4 years. Paper III. Early and delayed loading of full arch mandibular prostheses were evaluated in 109 patients, 54 with delayed loading and 55 with early loading, with a mean follow-up of 3.6 years. Paper IV. Submerged and non-submerged implant placement for supporting fixed prostheses in the edentulous mandible were evaluated after five years in 29 patients. Paper V. The precision of fit of CNC-milled I-Bridge^® frameworks was evaluated using two different implant systems.

Results: Paper I. The five-year cumulative survival rate (CSR) for implants was 99.1% and for prostheses 100%. Mean bone loss from baseline to five-year follow-up was 0.5 mm. No indication could be found that the number of supporting implants influenced the prosthetic complications. Paper II. The five-year implant and prosthesis CSR was 97.7% for two-implant supported FPDs and 97.3% for three-implant supported FPDs. Mean bone loss at five years was 0.4 mm. Significantly more prosthetic and abutment screw loosening were seen in two-implant supported FPDs. Paper III. Five-year CSR for implants was 94.4% and 92.5% for prostheses in early loading, and 97.9% and 98.0% in the delayed loading group. More prostheses needed adjustment or replacement in the early group, but patients treated with early loading were more pleased with the treatment procedure. Paper IV. Five-year CSR survival rate was 99.4%. Three implants fractured in one patient. Mean bone loss at five years was 0.7 mm in submerged implants and 0.5 mm in non-submerged implants. Paper V. All frameworks demonstrated clinically acceptable fitwith mean distortion values within 23 μm (x-axis), 26 μm (y), 4 μm (z- axis) and 34 μm (3-D) for all frameworks. Control frameworks displayed greater levels of distortion than frameworks produced in a strict test situation.

Conclusion: A reduction of the number of supporting implants to four implants in full arch mandibular prostheses and two implants in three unit FPDs in partial edentulous jaws resulted in the same clinical outcome as when more implants are used. Non-submerged implant placement in the edentulous mandible was as predictable as submerged, but early loading of implant-supported mandibular prostheses incurred more prosthetic complications. Computer numerical controlled milled frameworks presented levels of precision of fit within limits considered to be clinically acceptable and superior to earlier published results on cast frameworks.

Key words: Computer numerical controlled, dental implants, fixed prostheses, non-submerged

ISBN: 978-91-628-7467-4; ISSN: 0348-6672; Swedish Dental Journal Supplement 197, 2008

Correspondence: Alf Eliasson, Department of Prosthetic Dentistry, Postgraduate Dental Education Center Örebro, Sweden; email: alf.eliasson@orebroll.se

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List of Papers

I Eliasson A, Palmqvist S, Svenson B, Sondell K. Five-year results with fixed complete arch mandibular prostheses supported by 4 implants. Int J Oral Maxillofac Implants 2000; 15:505-510.

II Eliasson A, Eriksson T, Johansson A, Wennerberg A. Fixed partial prostheses supported by two or three implants: A retrospective study up to 18 years. Int J Oral Maxillofac Implants 2006; 21:567-574.

III Eliasson A, Blomqvist F, Johansson A, Wennerberg A. A retrospective analysis of early and delayed loading of full-arch mandibular prostheses using three different implant systems: Clinical results up to 5 years of loading. Clin Implant Dent Rel Res. In Press.

IV Eliasson A, Narby B, Ekstrand K, Hirsch J, Johansson A, Wennerberg A. A 5-year prospective clinical study of treatments with implant-supported fixed prostheses in the edentulous mandible using the Paragon System Implants placed according to a submerged and non-submerged surgical protocol. Submitted for publication.

V Eliasson A, Wennerberg A, Johansson A, Örtorp A, Jemt T. The precision of fit of milled titanium implant frameworks (I-Bridge^®) in the edentulous jaw. Submitted for publication.

Papers I and II are reproduced with permission from Quintessence Publishing Co. Inc., Hanover Park, Illinois.

Paper III is reproduced with permission from Blackwell Publishing Inc., Malden, MA 02148.

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Introduction

Background

Residual ridge resorption in patients wearing complete dentures is a problem that affects retention and stability of the denture. In order to improve support for prostheses and restore masticatory function, dental implants have been a topic for research for more than 60 years.

During the 1980´s and 1990´s studies were conducted with alveolar ridge augmentation procedures using hydroxylapatite and positive reports were published stating that 90% of the grafted ridges displayed negligible radiographic resorption and prosthesis function was improved.^1,2

The early metal dental implants were fabricated from various alloys or titanium and were principally of two types; subperiostal or endostal implants.^3-6 A third type of implant was the mandibular staple bone plate, a device used to restore the atrophic mandible.^7-10

The development of Brånemark system^® implants started in the 1960´s when Per-Ingvar Brånemark and co-workers initiated experiments with screw shaped dental implants fabricated from commercially pure (c.p.) titanium with a turned surface. In 1969 the group published results from animal studies concluding that in the dog threaded titanium fixtures could successfully be placed and loaded with axial and lateral forces for several years in both jaws.¹¹

New dental implants were also developed by others during the 1970’s. André Schroeder and the international team for implantology (ITI) research institute in Bern developed a dental implant system from c.p. titanium with a rough titanium plasma sprayed surface fabricated in various shapes; the implants were used to rehabilitate edentulous patients by means of overdentures supported by a Dolder bar.^12-15 In Germany, Willi Schulte developed a root formed implant system (Frialit) from the ceramic Al2O3; with incrementally increased diameters intended for replacing single teeth.¹⁶ The material in the implant was changed to c.p. titanium in 1990 and the name was subsequently changed to Frialit 2.

In 1977 the Brånemark group published their ten-year experience of 1618 dental implants placed in 128 upper and 107 lower jaws, laying the scientific foundation of modern dental implantology and introducing the concept of osseointegration.¹⁷ Further reports by Adell and colleagues promoted the wider acceptance of the Brånemark system^®implants.¹⁸ The first international team to learn Brånemark’s principles of osseointegration was a group led by George Zarb in Toronto who commenced the Toronto replica study in 1979, now one of the

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most important data banks on dental implants. A few years later Zarb initiated the Toronto conference (1982), where osseointegration was first presented and recognised as a reliable treatment possibility for edentulous patients. The proceedings of the Toronto conference were issued as a separate volume of reprints, edited by George Zarb, from the Journal of Prosthetic Dentistry.¹⁹ Another milestone in the dissemination and acceptance of the use of dental implants to support prostheses in edentulous patients was the book “Tissue integrated prostheses: osseointegration in clinical dentistry” edited by Brånemark PI, Zarb GA and Albrektsson T.²⁰

During the 1980´s and 1990´s many new implant systems were introduced on the market with sparse scientific documentation.¹³ In a review in 1991 Albrektsson and co-workers reported a lack of scientific support by adequate clinical reports of minimally 5-years of follow-up for many of the currently used implant systems and only one implant system presented 15 years’

follow-up in 1991.²¹ In a recent review Albrektsson & Wennerberg reported that more implants now had sufficient five-year data documenting good results and that the standard of clinical reporting had improved over the years. Yet in 2004 only one of the frequently used moderately rough surfaces, was documented for survival over 10 years of follow-up.^22,23

The development of the clinical procedures was divided into three periods by the Brånemark group; the “initial period” from July 1965 to March 1968, the “development period” April 1968 to June 1971 and the “routine period” starting in July 1971.^17,18 The three-year survival rates of implants reported by Adell and colleagues (1981) were 53% in the maxilla and 74%

in the mandible in the development group, compared with 82% and 91% respectively for the first routine group.¹⁸ The conclusions from the clinical trials resulted in a list of six prerequisites claimed to be the most important for predictable implant integration. These prerequisites have varied with authors and publications, Table 1.^11,24,25 Rehabilitation with implant-supported prostheses according to the Brånemark protocol during the 1980´s and early 1990´s resulted in many of the reports of successful rehabilitation of partially and totally edentulous jaws.^26-38

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Table 1. Prerequisites for osseointegration according to the Brånemark protocol as proposed by different authors.

Brånemark & colleagues -69 Albreksson & colleagues -81 Szmukler-Moncler &

colleagues 2000 1) Inert, mechanically and

chemically clean implant.

2) Implant size small enough to allow complete embedding in bone.

3) Atraumatic preparation of the bed of the implant.

4) Primary closure of the fixture site from the oral cavity until the barrier function of the tissue has been recovered after the operation. This biological barrier is formed by

approximation of hard and soft tissue to the implant.

5) Loading of the implant via a prosthesis result in remodeling of the jawbone.

6) Gingivitis with formation of inflammatory granulation tissue should not be allowed to develop or to persist.

1) Implant material, i.e.

titanium 2) Implant design 3) Implant finish 4) Status of the bone 5) Surgical technique 6) Implant loading conditions

1) Use of a biocompatible material, i.e. titanium 2) Use of a 2-stage procedure 3) Use of a stress-free healing period of 3–6 months before loading

4) Atraumatic surgery involving low-speed drilling

5) Use a mucobuccal incision and avoid a crestal one 6) Use of sterile conditions as

‘‘in a fully equipped operating theatre’’

7) Use of titanium ancillary 8) Avoid radiographs before the end of the healing period 9) Use of acrylic occlusal contact surfaces

Fixed prostheses

The titanium implants developed by professor Brånemark were used for supporting fixed prostheses in mainly edentulous patients receiving full arch fixed prostheses. During the development of the implant treatment procedures only totally edentulous jaws were treated, starting with edentulous mandibles but soon also edentulous maxillas. In the development group ending in 1968 half of the treated jaws were edentulous maxillas.¹⁷ Since the presentation of the successful use of implants supporting fixed prostheses in the 1970´s and 1980´s for edentulous maxillae and mandibles, it has become a standard procedure for decades.²⁶Numerous reports on the successful use of Brånemark system^® implants in the edentulous mandible with ten years’ follow-up or more have been published.26,35,39-43 Engfors and colleagues published a study on old patients, aged 79 years or more at implant placement, rehabilitated with fixed prostheses and achieving five-year cumulative implant survival rates of 93% in the maxilla and 99.5% in the mandible, the same survival rates as found in the

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younger control group.⁴⁴ According to published review articles the five-year implant and prosthesis survival/success rates have increased since the early studies and are now 96% - 100% in the mandible.^45-47

Few patients were treated with implant-supported fixed partial dentures (FPDs) in the early 1980´s but partially edentulous patients were increasingly rehabilitated with implant- supported prostheses during the 1980´s, which have since then become a routine procedure over the years.^48-52 Van Steenberghe reported in 1989 on a multicenter study on FPDs in 38 patients with 133 implants; the follow-up was fairly short (0.5 to 3.5 years) but the success rate reached 87% in the maxilla and 92% in the mandible. Fixed prostheses supported by teeth and implants were also introduced in the mid 1980´s when the remaining teeth were too few or unevenly distributed.^53-56 The use of combined implant and teeth supported prostheses has increased but few RCTs have been conducted. In systematic reviews of prosthesis and implant survival rate for FDPs supported by only implants and FDPs supported by implants and teeth, survival rates were lower for implants and prostheses supported by both teeth and implants than for prostheses supported by implants only.^57,58 The five-year implant and prosthesis survival rates were 95.4% and 95% respectively for implant-supported FPDs, and 90.1% and 94.1% for tooth-implant supported FPDs.^57,58

The use of implants for single tooth replacement was introduced in the mid 1980´s, as described by Jemt and Ohrnel.^59,60 Three-year results were presented by Jemt and colleagues in 1990.⁶¹ Today single teeth replacement by implants is advocated by some as the first option since it avoids preparation of sound neighboring teeth. Lindh and colleagues and Creugers and co-workers conducted meta-analyses on single implants reporting implant and crown survival rates of 97% to 97.5% for implants and 83% of crowns free of complications after four years.^62,63 Increasing interest in single tooth replacement has led to numerous reports on implant placement and bone augmentation techniques. Yet implant treatment in the esthetic zone is challenging, especially when more than one tooth is missing; thus submerged placement has been recommended in a consensus report by Belser and colleagues.^48,64

Retrievability

When placing full-arch prostheses supported by implants, retrievability may be important since complications with implants and prostheses are commonly reported in both the totally edentulous and partially edentulous jaw.^51,65-74 The most frequently reported problems with fixed full-arch prostheses are fracture of acrylic resin matrix and acrylic resin teeth, followed

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by abutment and prosthetic screw loosening and screw fractures. Fractures of frameworks and extensive wear of acrylic teeth have also been reported.^75-79

With the increasing use of Brånemark system^®implants in the rehabilitation of partially edentulous patients retrievability remained important and prostheses were mostly screw retained. In studies on FPDs the most frequently reported technical complications are chipping of the veneering porcelain and prosthetic or abutment screw loosening or fracture.^73,80-82Studies on implant rehabilitation often concentrate on implant and bone loss;

prosthetic complications are more seldom described.⁴⁵ According to meta-analyses performed by Lang and colleagues and Pjetursson and co-workers biological and technical complications are registered in 38.7% of the FPDs within five-years.^57,83

Meta-analysis articles and review articles on RCTs present 5-year survival rates for implants in the range of 95% - 97.5% and for FPDs 83% - 95%, and 92.8% and 86.7% respectively after ten years, with no major differences between implant systems.45,57,83,84

The influence of prosthetic and implant therapy on patient satisfaction and quality of life is a field of research still in development and there is often a lack of information concerning this aspect of implant-supported prostheses. In studies concerning these aspects cost is the least used outcome according to Strassburger and colleagues.⁸⁵

Numerous studies on implant treatments followed the guidelines presented by the Brånemark group, implant placement submerged, a healing period of three months in the mandible and six months in the maxilla, the placement of five or six implants in totally edentulous mandibles and maxillas and three or more implants in the partially edentulous situation, and fabrication of prostheses framework from gold alloy.

Several possible ways exist to reduce the cost of implant treatment with fixed prostheses. The number of implants used in totally and partially edentulous jaws may be reduced by one or two thus reducing cost for implant components as well as the time consumed for implant placement, and the prosthetic procedure will be facilitated. A change in surgical procedure, by using non-submerged healing, would shorten treatment time, and surgical interventions would be reduced reducing the cost of implant placement. If prostheses are immediate or early loaded the use of temporary prostheses after implant placement may be omitted, treatment time would be further reduced resulting in earlier oral rehabilitation and possibly reduced cost. The original treatment concept used frameworks cast in gold alloy, which inevitable results in a considerable cost for the framework. If non precious metals or alloys

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could be used the material cost would be significantly reduced and prostheses would become more affordable. The casting procedure of frameworks for implant-supported prostheses is difficult and sectioning and soldering often have to be performed; if industrial methods of framework fabrication could be used the manual labour content would be reduced as well as the cost.

The number of implants needed in different situations

Totally edentulous jaws

The number of implants needed in rehabilitation of totally edentulous jaws with fixed implant-supported prostheses has not been investigated in many studies. From the available literature few studies discuss the use of a reduced number of implants supporting a fixed prosthesis in the mandible. More studies have been performed on overdentures using a reduced number of implants; two instead of four implants for supporting overdentures in the mandible. The current literature shows no differences in bone loss and implant survival rates for implants supporting overdentures in the mandible whether there are two or four implants supporting the prosthesis and implant survival rate is generally within 96% to 99%.^86-91 The use of fewer than the traditionally prescribed six implants for supporting fixed prostheses in the edentulous mandible and maxilla has been addressed by Brånemark and co-workers, who in 1995 presented no significant difference in survival of prostheses and implants supported by four or six implants over a ten-year period.³⁹ Thirteen mandibles and fourteen maxillas with prostheses supported by four implants were included. Today, many specialist centres in Sweden use five implants in the edentulous mandible as a routine.⁹² With the use of only four implants cost will be reduced further and the prosthetic treatment and cleansing of the prosthesis may be enhanced.

Studies on load transfer and stress distribution by implant-supported prostheses show that when a cantilever prosthesis is loaded most of the load and stress are concentrated on the distal implant and only small stresses were seen at the implant third from the loaded cantilever.^93-95

Short-term studies on conventional and early loading of only four implants with fixed prostheses have presented encouraging results. Becker and colleagues reported 20 patients, receiving four to six Brånemark system^® implants each and loaded within five days, showing a two year cumulative survival rate of 96.5% for implants and 100% for the prostheses.⁹⁶

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Slightly less favourable results were described by Kronström and co-workers and Engqvist and colleagues.^97,98 Survival rates of 100% for early/immediate loading of four implants have been reported by Collaert and De Bruyn in 11 patients, Klee de Vasconcellos and co-workers in 15 patients and Capelli and colleagues in 24.^99-101 Reducing the number of implants in the maxilla has been investigated by Malóand colleagues, who reported implant and prosthesis survival rates after one-year of 97.5% and 100% respectively on four immediately loaded implants in the edentulous maxilla.¹⁰²

Studies of fixed prostheses supported by as few as three implants in the edentulous mandible, have reported implant survival rates of 90.5% to 97% after one-year, indicating that even as few as three implants may be sufficient for supporting a fixed full arch prosthesis in the mandible. However, if one implant is lost, the prosthesis must be adjusted or replaced with additional implant placements.^103-108

During the 1980´s and early 1990´s many reports of implant-supported fixed prostheses in the edentulous mandible followed the original Brånemark protocol with only minor changes in placement procedures. The reported five- and ten-year survival rates for implants and prostheses are in the range of 96% to 100%. The use of less than five implants in the rehabilitation of the edentulous mandible was rarely reported. However studies of stress distribution in the prostheses and at individual implants indicated that the number of implants placed between the distal implants on the right and left side may be of minor importance in stress reduction on the distal abutments. Thus evaluating fixed prostheses in the mandible supported by only four standard implants could provide information as to whether the number of implants can be reduced to four to further reduce cost and facilitate implant placement and prosthesis fabrication without harming the implant and prosthetic survival rate.

Partially edentulous jaws

Fixed partial dentures supported by implants have been used for 40 years; Brånemark and co- workers placed the first fixed partial dentures in 1968.¹⁰⁹ The numbers of implants used per prosthesis are not reported in many studies, but the mean number of implants is often less than three.33,82,110,111 The use of more than two implants is in accordance with the recommendations by Rangert and co-workers; who proposed that implants should if possible be placed in a tripod configuration in order to withstand non-axial forces better.¹¹² Different opinions exist and Buser & von Arx stated that in situations with three occlusal units missing and sufficient bone anatomy the standard solution should be two implants supporting a three-unit FPD, in

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order to reduce cost.⁴⁸ The use of only two ITI^® implants supporting a three-unit FPD finds some support in a finite element study by Iplikçioğlu and Akça, who found that two 10 mm long ITI^® 4.1 mm diameter implants supporting a three-unit FPD, had a similar stress distribution to three 3.75 mm diameter implants.¹¹³ On the other hand both Rangert and co- workers and Buser & von Arx suggested that cantilevers should not be used in order to avoid unfavourable bending movements and, if used, the cantilevers should preferably be placed medially.^48,112 Still, cantilevers have been used for various reasons; one being insufficient bone volume for additional implants. Reports on cantilever FPDs have been published by Wennström and colleagues and Romero and colleagues with an implant survival rate of 97%

in both studies and prosthesis survival rates of 92.3% and 98% respectively and no significant increase in bone loss in a short perspective.110,114,115 These reports are supported by the reviews from Lang and colleagues and Pjetursson and co-workers, who reported no significant differences in five-year survival rates for cantilever FPDs or conventional FPDs;

with survival rates of 92.5% and 93.8% respectively.^57,58

Numerous studies on implant-supported FPDs include some prostheses supported by only two implants: some of them reporting higher complication rates for two-implant supported prostheses. The increased complication rates mostly concern screw loosening but implant fractures have been reported.31,33,37,72-74,81,116,117

The reported incidence of failed/lost short implants differs between implant systems with more implant losses reported for short Brånemark system^®implants with a turned surface, than for ITI^®implants. 116,118-122 In their review article das Neves and colleagues reported a mean implant loss of 9.7% for 7 mm Brånemark system^®implants.¹²³ Conversely Maló and colleagues reported 100% survival for short implants with the TiUnite^™surface.¹²² Buser and Arx stated that the use of short implants is not contraindicated but one implant per FPD unit should be placed when short implants (6 or 8 mm) are used.⁴⁸

During the late 1980´s and 1990´s an increasing number of studies were published on implant-supported FPDs presenting five-year implant survival rates of 95% to 97.5% and 83% to 95% for prostheses. The ten-year survival rates were 92.8% and 86.7% respectively without dividing results between prostheses supported by two or more implants. Studies of implant and prosthesis outcome reported more technical complications with FPDs supported by only two implants than for those supported by three or more implants. Thus there is some scientific evidence supporting the use of two-implant supported FPDs. In the clinical situation anatomic structures sometimes reduce the available bone volume for implant placement; the

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choice is then either to perform bone augmentation procedures or to rely on a reduced number of implants placed. If bone augmentation procedures can be omitted without jeopardising the treatment outcome, surgical interventions and treatment time can be reduced as well as patient morbidity: with less surgical interventions and the use of only two implants cost can be reduced. Thus long-term follow-up studies of FPDs supported by two or three implants reporting implant and prosthesis complications and failure rates may provide support for the further use of two-implant supported FPDs.

Development of surgical techniques

Two major differences were seen between the implant systems developed by Brånemark and Schroeder. Firstly, the Brånemark system^® implants were finished with a turned surface and the ITI^® system with a rough titanium plasma sprayed surface. Secondly, the Brånemark system^® implants were two-pieced while the ITI^® was a one-piece implant. Whether theses differences made the implants more or less suitable for different surgical procedures have been investigated in animal and clinical studies over the years. As a result, implant placement procedures for two-piece implants have changed since the above prerequisites were stated.

The position of the incision (mucobuccal or crestal) has also been tested in Randomized Controlled Clinical Trials (RCTs). Coulthard and co-workers stated in their review in 2003 that few RTCs of the different techniques were available; but no differences in implant failures, marginal bone levels, morbidity or patient satisfaction were reported whether a mucobuccal or crestal incision was used.¹²⁴ Leaving the implants buried under the oral mucosa during the healing phase was one of the prerequisites to be challenged, since it was not used in the studies conducted by Schroeder and the ITI institute, who nevertheless achieved successful osseointegration with ITI^®implants. Reports of successful use of non- submerged ITI^® implants were increasingly published during the 1980´s and early 1990´s.^125-

130

Animal studies on one- and two-stage placement of dental implants

The different surgical protocols used by Brånemark and Schroeder were first tested in animal models prior to placing implants in humans. Since then an increasing number of studies on tissue response to implants has been conducted in animals.^131-140 Weber and co-workers and Fiorellini and colleagues undertook split mouth studies in Beagle dogs comparing the two surgical techniques and reported different bone loss during the healing phases; but at the end

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of the 18 week study no significant differences in bone levels were registered between one- and two-stage implant placement.^134,139

Histological evaluations of the soft tissue response to the two surgical techniques also present diverging results. Weber and colleagues reported significantly greater apical extension of the periimplant epithelium and significantly lower attachment level to submerged implants with second-stage transmucosal abutments than in non-submerged, one-stage implants.¹³⁴Others, on the other hand, described similar appearances at submerged and non-submerged implants.135,136,141 Abrahamsson and colleagues placed three different commercially available implant systems (Brånemark system^®, Astra Tech^® dental implant system and ITI^® dental implant system) in beagle dogs according to the recommendations of the respective manufacturer; histometric analysis of the mucosal barrier at the titanium surface after one- stage or two-stage installations identified similar dimensions and compositions at the three implant systems studied.¹⁴¹ However the mucosal barrier formed at implants and abutments may be compromised by repeated manipulation of the abutments. One shifting of abutments after second-stage surgery did not affect the dimension and quality but repeated disruption of the mucosal barrier resulted in a more "apically" positioned zone of connective tissue and additional marginal bone resorption.^142,143

Animal studies on loading of implants

Animal studies on the early bone-to-implant contact (BIC) against different titanium surfaces clearly showed that a moderately rough surface promotes bone healing in loaded and unloaded situations.^144-148 Piatelli and colleagues studied bone reactions to loaded and unloaded implants in monkeys and found that implants loaded after 30 days presented thicker lamellar and cortical bone at the neck of loaded implants.¹⁴⁹ Further studies in monkeys on immediate loading presented 100% implant survival and more BIC at loaded implants than unloaded controls.^150-152

Tests of loading of osseointegrated implants have been performed using both static and dynamic loads. In studies by Gotfredsen and colleagues, static loading of implants in the dog did not cause any significant changes in bone loss compared to unloaded implants but displayed signs of a structural adaptation.146,153,154 Berglundh and colleagues used a dog model to demonstrate increased BIC in loaded implants but no difference in bone level between loaded implants and controls; diverging results were presented by Duyck and colleagues who noted no adverse effects to static load but a crater like bone defect lateral to

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implants subjected to excessive dynamic load.^148,155Isidor presented similar results from a monkey study when excessive lateral loading was applied to the implants, reporting implant mobility after 4.5 months for two of the eight test implants and additional three implant losses after 15.5 months.¹⁵⁶

Clinical studies on one- and two-stage placement of dental implants

Implant studies on the ITI^® implant system have consistently used non-submerged placement in partially and totally edentulous patients with good results, and submerged healing has only been advocated in sites with esthetic priority. 48,125,127,157 Since the mid 1990´s an increasing number of studies of non-submerged placement of two-piece implants have reported success figures comparable to the traditional submerged implant placement procedure.^92,158-165 Diverging results were reported by Røynesdahl and colleagues and Fenlon and co-workers who reported increased implant losses when turned implants were placed non-submerged in the anterior mandible.^166,167 A slightly less successful use of non-submerged Brånemark system implants in the edentulous mandible was also reported by Becktor and colleagues in a prospective multicenter study on one- and two-stage implant placement in 77 patients, with survival figures of 91.4% for one-stage surgery and 97.6% for two-stage implant placement.¹⁶⁸ Petersson and colleagues undertook a five-year study with three different treatment concepts; submerged, non-submerged implant placement with conventional loading and non-submerged implant placement with early loading.¹⁶⁹ After prosthesis connection bone loss was significantly lower in the early functional loading group compared to the one- and two-step surgical technique groups, but after 18 months and after 5 years no differences remained.¹⁶⁹ In a recent review by Esposito and colleagues three RTC trials of submerged and non-submerged implant placement were identified; two of them with a total of 45 patients were included in the analysis. From these trials, on a patient, rather than per implant basis, there were no statistically significant differences.¹⁷⁰ The authors’ conclusion was; “The number of patients included in the trials was too small to draw reliable conclusions but it appears that the two procedures did not show clinically significant differences. If these preliminary results will be confirmed by more robust trials, a one-stage procedure might be preferable since it avoids one minor surgical intervention and shortens the waiting time to provide the final restoration”. Non-submerged implant placement reduces the time consumed by implant placement procedures, thus reducing the cost of surgery. Prosthetic treatment may also be facilitated by the presence of healed periimplant tissue at impression making, which

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may decrease the need for later adjustments of the prostheses to optimize prosthesis adaptation to the soft tissue. Cecchinato and colleagues published two-year results of a multicenter randomised controlled trial on submerged and non-submerged placement of Astra tech^®implants in the posterior part of the dentition, reporting 2.1% early implant losses with no differences between the groups and bone loss less than 0.1 mm in the non-submerged group and 0.2 mm in the submerged group.¹⁶⁵ Moberg and colleagues compared treatment of mandibular edentulism with submerged and non-submerged implants presenting cumulative success rates of 97.9% and 96.8% for the two techniques.¹⁷¹

In spite of numerous published studies on implant rehabilitation with the different surgical techniques, some studies report lower survival figures for implants with turned surfaces placed non-submerged; the reason for this is not elucidated. Few RCTs have been published confirming that the implant placement technique (submerged or not-submerged) does not effect implant survival rate and bone loss between the two techniques. A split mouth RCT may add further scientific evidence for the use of non-submerged implant placement in the anterior part of the edentulous mandible.

Loading of implants

There are different opinions on when a dental implant is loaded; some consider the implant as loaded when placed submerged buried by the mucosa but subjected to loading through the mucosa by chewing food with or without removable prostheses. Others consider the implant as loaded when it penetrates the oral mucosa and becomes visible in the oral cavity, regardless of whether it is a cover screw or healing abutment that is visible. Theoretically different types of load can now be applied to the implant, such as pressure from tongue and cheek, food pressing on top of the implant or a removable prosthesis leaning on or gripping the implant component. Other investigators suggest that the implant is loaded when a temporary prosthesis or implant component is placed onto the implant and protrudes into the oral cavity but not in occlusion with the opposing dentition. Finally, some authors consider the implant as loaded when a temporary or final implant restoration is in direct contact with the opposing dentition, which may be a more objective measurement according to Cochran.¹⁷²

Non-submerged implant placement simplifies rehabilitation of edentulous patients by reducing the surgical interventions. With the acceptance that two-stage surgery was not a pre-

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requisite for implant osseointegration, focus was turned on the time of healing before loading.

If implants can be loaded early or immediately a considerable reduction in treatment time can be achieved and the use of removable temporary prostheses during the healing phase can be omitted. In order to have a universal understanding of the meaning of immediate, early and delayed loading, this issue has been addressed at different consensus conferences and there- after reported by groups of authors presenting diverse lists of definitions, Table 2.^173-175

Table 2. Consensus statements concerning loading protocols.

Aparicio et al. 2003 Cochran et al. 2004 Misch et al. 2004 Immediate loading:

The prosthesis is attached to the implants the same day the implants are placed.

Early loading: The prosthesis is attached at a second procedure, earlier than the conventional healing period of 3 to 6 months; time of loading should be stated in days/weeks.

Delayed loading: The prosthesis is attached at a second procedure after a conventional healing period of 3 to 6 months.

Immediate restoration: A restoration inserted within 48 hours of implant placement but not in occlusion with opposing dentition

Immediate loading: A restoration placed in occlusion with opposing dentition within 48 hours of implant placement Early loading: A restoration in contact with the opposing dentition and placed at least 48 hours after implant placement but not later than 3 months afterward.

Conventional loading: The prosthesis is attached at a second procedure after a healing period of 3 to 6 months.

Delayed loading: The prosthesis is attached in a second

procedure that takes place sometimes later than the conventional healing period of 3 to 6 months.

Immediate occlusal loading: Immediate occlusal loading within 2 weeks of implant insertion.

Early occlusal loading: Occlusal load to an implant prosthesis between 2 weeks and 3 months after implant placement.

The actual time may use the number of weeks in parentheses (ie, early (5 weeks) occlusal loading).

Non functional immediate restoration: An implant prosthesis in a patient who is partially edentulous delivered within 2 weeks of implant insertion with no direct occlusal load.

Non functional early restoration: An implant restoration delivered to a patient who is partially edentulous between 2 weeks and 3 months after implant insertion.

Delayed or staged occlusal loading:

Occlusal loading to an implant restoration more than 3 months after implant insertion.

Two-stage delayed occlusal loading The soft tissue covers the implant after placement. A second stage surgery after 3 months exposes the implant to the oral environment.

One-stage delayed occlusal loading The implant is positioned slightly above the soft tissue during the initial implant placement. The implant is restored into occlusal load after more than 3 months.

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Development of loading protocols

The loading protocol used during the first decade after the Toronto conference was in most cases, in accordance with the recommendations by Brånemark, with three months of submerged healing in the mandible and the six months healing in the maxilla.¹⁷ Some support for this was gained by results on bone healing at dental implants presented by Roberts, who suggested that endosseous implants could be provisionally loaded at about 18 weeks, but full maturation of the implant interface required approximately one year.¹⁷⁶

The increasing use of different dental implants during the 1980´s and 1990´s resulted in observations that implants could be loaded earlier than the proposed three or six months in the mandible or maxilla. Szmuckler-Moncler and colleagues reviewed the literature concerning timing of loading and reported diverging results; from early animal studies presenting fibrous encapsulation of implants subjected to early loading to later studies presenting osseointegration in implants immediately loaded.¹⁷⁷ The conclusion made was that the absence of loading per se was not critical for osseointegration but rather the absence of excessive micromovements at the bone-implant interface. Micromovements of 50 micron (µm) were tolerated, and micromovements up to 150 µm may be tolerated. The tolerated thresholds varies according to surface and/or implant design and may be as high as 150 µm;

thus a long stress-free healing period may not be mandatory to achieve osseointegration for splinted screw shaped implants.¹⁷⁷ The amount of loading that result in these levels of micromotions depends on several factors; such as the masticatory forces, bruxism, bone quality and quantity, implant length, length of cantilever, implant shape and surface, surgical skill and placement technique. In order to avoid heavy loading of individual implants it has been advocated that the implants should be rigidly connected, either with a bar construction supporting an overdenture or a fixed prosthesis.

Implant-supported overdentures

Implant-supported overdentures are a treatment option which significantly improves prosthesis function at a lower cost than fixed implant-supported prostheses. In a survey of the use of mandibular implant overdentures in ten countries the frequency of implant overdentures ranged from 7% in Japan to 81% in the Netherlands.¹⁷⁸ Treatment cost was reported as the main reason for choosing overdentures instead of fixed prostheses.

The successful use of implant-supported overdentures has been reported in several clinical studies with ten to twelve years’ follow-up presenting implant survival rates of 90% to 97.2%,

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with no difference in treatment outcome for splinted or unsplinted implants. 91,179,180 The first to describe immediate loading of implants was Ledermann, who in 1979 reported on implants loaded with an overdenture supported by a bar construction.¹⁸¹ In a multicenter study comprising 226 patients, Chiapasco and colleagues reported on the use of immediate loading of implant-supported mandibular overdentures, presenting 96.9% survival of the implants and 98.5% on the prostheses. Since then many reports have been published on immediate and early loading of implant-supported overdentures in the edentulous mandible, presenting survival rates from 96.1% to 100% in studies with a follow-up time ranging from one to five years.^182-187 In 2000, Szmukler-Moncler and colleagues stated that “It is shown that successful premature loading protocols require a careful and strict patient selection aimed to achieve the best primary stability”.²⁵ In 2004 Chiapasco and Cochran and colleagues in review articles on early and immediate loading of implants in completely edentulous patients, reported implant survival rates ranging from 96% to 100% for immediate loaded overdentures and Cochran and colleagues stated that “immediate loading of four implants in the interforaminal area with rigid bar fixation and cross arch stabilisation is a predictable and well documented procedure”.^174,188 Scientific evidence for early loading was less substantial, in the reviews by Chiapasco and Cochran and co-workers only six publications with a total of 85 patients were identified and included.^174,188 In 2006, Del Fabbro and colleagues published a review including 14 studies on immediate loading of overdentures, reporting implant survival rate of 95.1% for the immediate loaded implants of which 96.5% had a rough surface.¹⁸⁹ During 2007 three review articles were published on the subject different times of loading, concluding that it is possible to successfully load dental implants immediately though not all clinicians may achieve optimal results, careful case selection, meticulous surgery and proper design of prostheses are essential for optimal outcomes.^190-192

Fixed full arch prostheses

Immediate loading

The first reports on immediately loaded fixed interim implant-supported prostheses was published in 1990 by Schnitman and colleagues reporting on the outcome of seven patients provided with a fixed temporary prosthesis supported by three implants during the healing phase of the additional three or four submerged implants.¹⁹³ In a ten-year follow-up study of ten cases survival rate for immediate loaded implants was 84.7% and 100% for the delayed loaded implants.¹⁹⁴ Different solutions have been utilised with the introduction of immediate

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loading using fixed interim prostheses such as converted complete dentures, new acrylic prostheses or acrylic resin prostheses with a metal inner casting. 182,195-200 In a review Morton and colleagues suggested that the influence of cantilevers should be reduced by using an appropriate number of implants and by optimizing distribution.²⁰¹ The number of patients, implants placed in each patient and the number of immediately loaded implants varies between studies. The study populations in some of the early studies are small, ten to fifteen patients in each study, with a reported survival rate of 80% to 98.3% after one to two years.^195-197 Ibañez and colleagues reported on immediate loading of both maxillas and mandibles, presenting a 99.4% success rate after a follow-up of 6 to 72 months; the same survival rate was reported by Testori and colleagues in edentulous mandibles.^198,200

The first attempt to decrease the cost of rehabilitation of the edentulous mandible with a fixed prosthesis was made by professor Brånemark with the introduction of the Brånemark Novum^® concept (Nobel Biocare AB), consisting of a prefabricated titanium framework supported by three wide body implants. Implant placement was performed using a surgical template and the prosthesis was delivered on the same day or the day after. The results achieved with this technique showed that three implants are sufficient to support full-arch prosthesis in the edentulous mandible.¹⁰³ One-year results for the concept have been reported by Engstrand and co-workers and Henry and colleagues in 94 and 51 patients respectively, with implant survival rates of 95% and 91% respectively.^105,202 Hatano and colleagues developed a technique for prosthesis fabrication for immediate loading using three standard Brånemark system^® implants with a customised metal framework fitted with acrylic resin teeth and delivered the same day.¹⁰⁶ An implant survival rate of 97.6% was reported on 43 patients after 3 to 49 months.

In a review by Cochran including 16 studies with a total of 387 patients the reported implant survival rate ranged from 80% to 100% with a mean of 95%; the conclusion was that

“immediate loading of implants in the edentulous mandible is a predictable and well documented procedure provided that a relatively large number of implants are placed”.¹⁷⁴ Two years later a review by Del Fabbro and colleagues included 25 studies with a total of 593 mandibles; the mean number of implants supporting the prostheses was 4.54 and an implant survival rate of 97.2% was reported.¹⁸⁹ Of the included studies, 179 mandibles were treated with three Brånemark implants supporting full-arch prostheses.

Reports on immediate loading in the edentulous maxilla have increased in the last few years;

in a review in 2004 of immediate loading of edentulous maxillas with fixed prostheses only five studies with a total of 30 patients were included.¹⁸⁸ Two years later, Nkenke and Fenner

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their review of immediate loading included nine studies with a total of 164 patients treated with immediately loaded implants in the maxilla, with survival rates ranged from 83.3% to 100%.⁴⁶ Del Fabbro and colleagues in the same year included 16 studies of immediate loading of edentulous maxillas, presenting mean implant survival of 98.2%, with significantly lower success rates for implants with turned surfaces.¹⁸⁹ Bergkvist and colleagues and Östman and co-workers reported similar one-year implant survival rates.^203,204

Early loading

Henry and Rosenberg in 1994 reported on single-stage surgery and early loading of four Brånemark system^® implants with a fixed prosthesis in the edentulous mandible in five patients.²⁰⁵ Eriksson and colleagues in 2000 presented five-year results of early loading of implants in the anterior mandible with a fixed prosthesis, reporting 100% survival for implants in both test (16 patients) and control groups (11 patients).²⁰⁶ In a review by Chiapasco in 2004 only six studies were included with a total of 51 patients and 274 implants.

Survival of implants ranged from 90.5% to 100% with a mean of 97.3%.¹⁸⁸ Since then reports on larger patient populations have been published; Engquist and colleagues reported on 26 patients provided with 104 Brånemark system^®implants with a turned surface supporting fixed prostheses in the mandible. The reported three-year implant survival rate was 93.3%.⁹⁷ In 2005, Friberg and colleagues reported on 152 patients provided with 750 Brånemark system^®implants with a turned surface and prostheses loaded with a mean of 42 days after implant placement, presenting a one-year implant survival rate of 97.5%.²⁰⁷ In 2008, Friberg and Jemt reported on 90 patients provided with 450 Brånemark system^®implants with a TiUnite™ surface reporting a one-year survival rate of 100%.²⁰⁸

Few publications report prosthetic complications and maintenance procedures during the first years in function or modification of the prosthesis to accommodate the soft tissue. Reports on early loading in the maxilla were also sparse in 2004; Chiapasco found only four studies with a total of 26 patients supporting the use of early loading of implants in the edentulous maxilla with a fixed prostheses; presenting 89% to 100% survival rate after one to five years.¹⁸⁸Since then more studies have been published supporting early loading in the maxilla; Nordin and co-workers reported on 53 consecutively treated patients of whom 20 were treated with fixed prostheses in the edentulous maxilla; only 0.9% of the implants were lost.²⁰⁹ Fisher and Stenberg reported a prospective controlled study with a 100% success rate in the 16 tests and 8 control cases after three years of loading.²¹⁰ Nordin and colleagues reported early loading of

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maxillary implants in fresh extraction sockets in 19 patients; after two to three years the survival rate was 98%.²¹¹

The use of immediate and early loading has proven to be effective in short follow-up studies when a strict surgical and loading protocol has been utilized. From a biological point of view immediate loading of splinted implants may be a safer procedure than early loading, in which the implants are left unsplinted and subjected to uncontrolled loading from a temporary removable prosthesis until delivery of the final prosthesis. Furthermore, a fixed intermediate restoration can preferably be fabricated with a reduced cantilever; thus reducing the risk of overloading the implants during the healing phase. On the other hand, using a temporary prosthesis during the healing phase leads to fabrication of two prostheses; one interim and one definitive prosthesis three to six months later; inevitable increasing the cost. Conversely, by starting fabrication of the final prosthesis at or shortly after implant placement the final prosthesis can be delivered within two to six weeks; thus reducing treatment time and maybe treatment cost. Whether this can be performed with results comparable to conventional loading concerning biological and technical complications is under researched; and many have not investigated the cost of treatment. Further studies comparing results achieved with early loading and delayed loading may provide additional information as to whether this is cost effective or not.

Impression and model fabrication for implant-supported prostheses

Rehabilitation with implant-supported prostheses requires many different steps before placement of the prostheses. Distortion in the final prosthesis can be due to some of the following; inaccuracy of the interface relationship between implant components, distortion introduced by the impression material and/or technique, fabrication of the model and choice of stone plaster used for fabrication, waxing and casting techniques. Different impression materials and techniques have been tested during the years, with no material producing an exact copy of the positioning of the implants/abutments but polyether and addition silicone produce similar results with little distortion if handled properly.^212,213 Today polyether, polyvinyl siloxane or plaster impression material are the most used.

Impressions can be made with impression copings for either indirect or direct technique.

Direct technique implies that the transfer coping is removed from the abutment/implant with the impression on removal. The technique can be used with a closed tray and transfer copings

On the role of number of fixtures, surgical technique and timing of loading

On the role of number of fixture, surgical technique and timing of

loading

Alf Eliasson

Gothenburg 2008

On the role of number of fixture, surgical technique and timing of

loading

Alf Eliasson

Gothenburg 2008

On the role of number of fixtures, surgical technique and timing of

loading

List of Papers

Contents

Introduction